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chemistry. 5.3. Light. Light How are the wavelength and frequency of light related?. 5.3. Light. The amplitude of a wave is the wave’s height from zero to the crest. The wavelength , represented by (the Greek letter lambda), is the distance between the crests. 5.3. Light.
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5.3 Light • Light • How are the wavelength and frequency of light related?
5.3 Light • The amplitude of a wave is the wave’s height from zero to the crest. • The wavelength, represented by (the Greek letter lambda), is the distance between the crests.
5.3 Light • The frequency, represented by (the Greek letter nu), is the number of wave cycles to pass a given point per unit of time. • The SI unit of cycles per second is called a hertz (Hz).
5.3 Light • The wavelength and frequency of light are inversely proportional to each other.
5.3 Light • The product of the frequency and wavelength always equals a constant (c), the speed of light.
5.3 Light • According to the wave model, light consists of electromagnetic waves. • Electromagnetic radiation includes radio waves, microwaves, infrared waves, visible light, ultraviolet waves, X-rays, and gamma rays. • All electromagnetic waves travel in a vacuum at a speed of 2.998 108 m/s.
5.3 Light • Sunlight consists of light with a continuous range of wavelengths and frequencies. • When sunlight passes through a prism, the different frequencies separate into a spectrum of colors. • In the visible spectrum, red light has the longest wavelength and the lowest frequency.
5.3 Light • The electromagnetic spectrum consists of radiation over a broad band of wavelengths.
5.3 Atomic Spectra • Atomic Spectra • What causes atomic emission spectra?
5.3 Atomic Spectra • When atoms absorb energy, electrons move into higher energy levels. These electrons then lose energy by emitting light when they return to lower energy levels.
5.3 Atomic Spectra • A prism separates light into the colors it contains. When white light passes through a prism, it produces a rainbow of colors.
5.3 Atomic Spectra • When light from a helium lamp passes through a prism, discrete lines are produced.
5.3 Atomic Spectra • The frequencies of light emitted by an element separate into discrete lines to give the atomic emission spectrum of the element. Mercury Nitrogen
5.3 An Explanation of Atomic Spectra • An Explanation of Atomic Spectra • How are the frequencies of light an atom emits related to changes of electron energies?
5.3 An Explanation of Atomic Spectra • In the Bohr model, the lone electron in the hydrogen atom can have only certain specific energies. • When the electron has its lowest possible energy, the atom is in its ground state. • Excitation of the electron by absorbing energy raises the atom from the ground state to an excited state. • A quantum of energy in the form of light is emitted when the electron drops back to a lower energy level.
5.3 An Explanation of Atomic Spectra • The light emitted by an electron moving from a higher to a lower energy level has a frequency directly proportional to the energy change of the electron.
5.3 An Explanation of Atomic Spectra • The three groups of lines in the hydrogen spectrum correspond to the transition of electrons from higher energy levels to lower energy levels.
5.3 Quantum Mechanics • Quantum Mechanics • How does quantum mechanics differ from classical mechanics?
5.3 Quantum Mechanics • In 1905, Albert Einstein successfully explained experimental data by proposing that light could be described as quanta of energy. • The quanta behave as if they were particles. • Light quanta are called photons. • In 1924, De Broglie developed an equation that predicts that all moving objects have wavelike behavior.
5.3 Quantum Mechanics • Today, the wavelike properties of beams of electrons are useful in magnifying objects. The electrons in an electron microscope have much smaller wavelengths than visible light. This allows a much clearer enlarged image of a very small object, such as this mite.
5.3 Quantum Mechanics • Classical mechanics adequately describes the motions of bodies much larger than atoms, while quantum mechanics describes the motions of subatomic particles and atoms as waves.
5.3 Quantum Mechanics • The Heisenberg uncertainty principle states that it is impossible to know exactly both the velocity and the position of a particle at the same time. • This limitation is critical in dealing with small particles such as electrons. • This limitation does not matter for ordinary-sized object such as cars or airplanes.
5.3 Quantum Mechanics • The Heisenberg Uncertainty Principle
5.3 Section Quiz. • 5.3.
5.3 Section Quiz. • 1. Calculate the frequency of a radar wave with a wavelength of 125 mm. • 2.40 109 Hz • 2.40 1024 Hz • 2.40 106 Hz • 2.40 102 Hz
5.3 Section Quiz. • 2. The lines in the emission spectrum for an element are caused by • the movement of electrons from lower to higher energy levels. • the movement of electrons from higher to lower energy levels. • the electron configuration in the ground state. • the electron configuration of an atom.
5.3 Section Quiz. • 3. Spectral lines in a series become closer together as n increases because the • energy levels have similar values. • energy levels become farther apart. • atom is approaching ground state. • electrons are being emitted at a slower rate.
